The invention relates to an electromagnetically actuated valve according to the species of the main claim.
Electromagnetically actuated valves are already known in the form of fuel injection valves, in which, for the purpose of reducing in the valve seat area the rebound behavior of a valve-closure member that is connected to a valve needle, and thus to avoid unwanted openings of the valve, a magnet armature is arranged on the valve needle so as to be relatively movable in relation to it.
German Patent Application No. 33 14 899 describes an electromagnetically actuated fuel injection valve, in which, for electromagnetic actuation, a magnet armature cooperates with an electrically excitable solenoid coil, and the stroke of the magnet armature is transmitted via a valve needle to a valve-closure member. To form a valve seal, the valve-closure member cooperates with a valve seat. The magnet armature is not rigidly secured on the valve needle, but is arranged so as to be movable in the axial direction relative to the valve needle. A first restoring spring acts upon the valve needle in the closing direction and therefore keeps the injection valve closed in the zero-current, nonexcited state of the solenoid coil. The magnet armature is acted upon in the stroke direction by a second restoring spring such that the magnet armature, in the resting position, contacts a first limit stop provided on the valve needle. In response to the excitation of the solenoid coil, the magnet armature is pulled in the stroke direction and, via the first limit stop, takes the valve needle with it. When the current exciting the solenoid coil is switched off, the valve needle is accelerated in its closing position by the first restoring spring and, via the described limit stop, takes the armature with it. As soon as the valve-closure member contacts the valve seat, the closing motion of the valve needle is abruptly terminated. The motion of the magnet armature, which is not rigidly connected to the valve needle, continues opposite to the stroke direction and it is absorbed by the second restoring spring, i.e., the magnet armature swings through against the second restoring spring, having a significantly weaker spring tension in comparison to the first restoring spring. Finally, the second restoring spring accelerates the magnet armature once again in the stroke direction. If the magnet armature meets the limit stop of the valve needle, this can lead to a new short-term lifting off from the valve seat of the valve-closure member, that is joined to the valve needle, and therefore to a short-term opening of the valve.
German Patent Application No. 33 14 899 describes a fuel injection valve having an armature that is fixedly joined to the valve needle, and a movable auxiliary mass. In this valve, two restoring springs are provided, specifically a first restoring spring as a spiral spring for the valve needle having the armature, and a second restoring spring as a disk spring for the auxiliary mass. The auxiliary mass, in the closed state of the valve, contacts a valve body that is fixed to the housing, so that between a limit stop disk of the valve needle and the auxiliary mass a distance remains when the valve is closed. After switching on the exciting current, the armature and therefore the valve needle rigidly joined to it are pulled against the force of the spiral spring. After one portion of the valve needle path has been traversed, the limit stop disk of the valve needle impacts against the auxiliary mass, the spring tension of the spiral spring adding to the spring tension of the disk spring. Towards the end of the pulling motion, the armature strikes against the magnetic pole and rebounds. The auxiliary mass can continue its motion against the force of the disk spring, as a result of which pressure is removed from the armature and a high excess of magnetic force is made available for braking the rebound motion. After switching off the magnet, the armature, or the valve needle, is reset by the combined force of the two springs.
In U.S. Pat. No. 5,299,776, connection with reducing the rebound action, describes joining the magnet armature to the valve needle in a nonrigid fashion, but rather to make it possible for the magnet armature to have a certain axial play at the valve needle. However, the axial position of the magnet armature in the resting position of the fuel injection valve is not defined in this embodiment, and therefore, in the valve, the response time in switching on the exciting current is undetermined.
Independent of electromagnetically actuated valves of this type having a magnet armature that is axially movable on the valve needle, for reducing or eliminating the rebound of the valve needle on the valve seat, electromagnetically actuated valves, e.g., in the form of fuel injection valves, are conventional, in which the magnet armature, the valve needle, and the valve-closure member constitute a rigid, axially movable valve element. In conventional valves of this type, often used for fuel injection in motor vehicles, one of the most essential objectives lies in accelerating this valve element as quickly as possible (in the order of magnitude of 0.2 to 1 ms) from the resting position, contacting the valve seat in the closed position of the valve. For this purpose, in the driving phase, a very high energy momentum must be applied, which makes necessary a short-term, very high booster current of significantly greater than 10 A at 120 V, for pulling the valve needle loose. This high booster current for its part can only be achieved in such valves using extraordinary electrical measures (costly electronic circuitry). These measures become all the more comprehensive, the higher the fuel counterpressure is (e.g., in direct fuel injection).
The electromagnetically actuated valve according to the present invention has the advantage that the valve needle is pulled loose and therefore the opening of the valve takes place in at least the same time or even faster than 0.2 ms, and for this purpose, in an advantageous manner, it is not necessary to have any high current peaks of a booster current. By applying mechanical momentum on the valve-needle by a movable auxiliary body, a system is described that is very simple in its design, and for which significantly simpler electronic circuitry is required for excitation than in the case of the conventional electromagnetic systems in valves.
As a result of the measures described advantageous refinements and improvements of electromagnetically actuated valves are possible.
Further advantages are also to be derived from the following description of the exemplary embodiments.